Cutting consumption by 40% doesn't automatically mean commuting only three days a week. Since the 1970s, the distance that people travel to work has been slowly creeping up. A large chunk of the necessary future conservation is presumably going to come from people living nearer where they work.

Right. The biggest single improvement the average person can make in their energy use is to carpool or take transit to work. A reduced availability of gasoline will promote carpooling and transit before it promotes the three-day week.

Agreed, and going to motor scooters instead of huge-tire pickup trucks will also help.
http://home.entouch.net/dmd/Oilcrisis.htm

I have the Vespa GTS250ie. I am very happy with it. http://www.vespaportland.com/vespa_gts250.htm

It is well-built, gets about 70 mpg if you are conservative in your driving around town, but is capable of highway speeds. Insurance is about $160/yr. The price however, has crept up about 10% since I bought mine in June.